1. Field of the Invention
This invention relates to a planar filter of microwave signal bands in a microstripline. More particularly, this invention relates to an interdigital filter having a superstrate and a substrate, the superstrate having a high dielectric constant and a high Q.
2. Description of the Prior Art
In mobile communication systems, numerous cellular telephones at the 800 MHz band have been put into practical use and, recently, the demand for hand-held cellular type mobile communication sets has been increasing. In terms of size, loss and cost reduction of known filters, antenna filters and RF stage filters are the most important RF passive components. Filters using dielectric resonators have the greatest advantage based on cost and physical size. However, such dielectric resonator filters are still expensive and the resonators must have a very high dielectric constant. Previous filters are more expensive to manufacture, are too large in size and are incapable of producing the same level of advantageous results as produced by filters of the present invention.